Air conditioning



April 1940- A. B. NEWTON 2,195,781

AIR CONDITIONING Filed Sept. 29, 1936 2 Sheets-Sheet 1 mi %& db:

Gttomegs Patented Apr. 2, 1940 UNITED STATES PATENT. OFFICE AIRCONDITIONING poration of Delaware Application September 29, 1936, SerialNo. 103,209

26 Claims.

This invention relates to air conditioning and more particularly tocooling and dehumidifica- "tion under summer conditions.

Prior to my invention it has been proposed to pass the air to beconditioned successively over two refrigerative evaporators from whichrefrigerant is drawn by a constant speed compressor and to whichrefrigerant is admitted through automatic expansion valves of thesuperheat control type. When there is demand for cooling, or fordehumidification'or both, the compressor is kept in operation, butwhenever the demand is for dehumidification alone one of the evaporatorsis cut out of the refrigerative circuit. The effect is to evaporate lessrefrigerant, but at a lower-suction pressure, so that not only is thetotal cooling effect on the air less than when both evaporators operate,but more moisture is" condensed from the air because the singleevaporator operates at a lower temperature. In other words, the sensiblecooling diminishes not only because of the reduction of totalrefrigerant evaporated, but also because a larger proportion of therefrigeration then effective is devoted to the extraction of latent heatfrom the water vapor carried by the air.

Regulation of this sort is commercially satisfactory but has thedisadvantage that some sensible cooling is a necessary incident todehumidification, whereas it is preferable to secure dehumidificationwithout sensible cooling when humidity alone is high.

According to the present invention, the air preferably contacts theevaporators serially andv in such case the second evaporator is the onecut out during simple dehumidification. At such times the secondevaporator is temporarily converted into a condenser for at least a partof the refrigerant compressed by thecompressor. While it so operates itserves as a reheater for the air cooled by the first evaporator, andrestores to the air at least a part of the heat extracted by the firstevaporator. The air thus is first cooled and then reheated, thetemperature dip serving to remove moisture without substantial finalchange in sensible heat, or at any rate with lessfreduction than is hadwith the described prior art arrangements. H in the present inventionthe use of a constant 50 speed compressor is preferred because it is thesimplest way known to applicant, to reduce evaporator temperature andincrease the dehumidifying effect when evaporative capacity isredguiced. Other functionally equivalent means for r noing evaporativetemperature are known and may be substituted, within the scope of thisinvention. Moreover, since some dehumidification is secured at normalevaporator temperature, reduction of evaporator temperature is notessential to practice of the invention in its broadest aspectl.

While the principal feature of novelty is that above described, thereare ancillary features, particularly as to the arrangement of theautomatic expansion valve, the control connections, etc., which will beappreciated as the detailed description proceeds.

The system is also favorably constituted for the inclusion in. theinstallation of means for heating and humidifying under winterconditions, and can be made to operate with success between seasons whenconditions shift back and forth between heating and coolingrequirements; Such an arrangement will be disclosed as a modifiedembodiment.

In the drawings,

Fig. 1 is a diagram of a very simple embodiment of the inventionintended solely for conditioning in summer.

Fig. 2 is a diagram of a similar system including means for conditioningin winter, and controls which will operate between seasons to select andregulate the action of the system according to demand.

Fig. 3 is a section of an automatic expansion valve used in bothembodiments above described.

For simplicity the invention will be described as embodied in a systemin which air withdrawn from the room is conditioned and returned to theroom, but nothing in the invention precludes its use with air circuitsin which all or any part of the air supplied to the conditioner is freshair. In other words, these various well known arrangements areequivalents, so far as the invention is concerned.

Similarly, the controls responsive to room condition are shown locatedin the room, but their location at any point at which they would respondto room conditions, for example in the return air duct, falls within thescope of the invention.

Further, while particular electrical controls will be described in somedetail, temperature and humidity control systems different in structurebut essentially similar in effect are well known andsubstitution ispossible. For example, thermostats of the pneumatic type are highlydeveloped and can be arranged to parallel the functions of theelectrical type chosen for illustration. Since the inventioniresides inthe way the controls are applied so as to be properly coordinated, andnot in the mechanics of the control devices themselves, applicant isentitled to a considerable range of equivalents.

In the embodiments shown the air passes serially over the twoevaporators, and this arrangement is preferred, because whendehumidifying without substantial ultimate cooling substantially all theair is first dehumidified and then substantially all is reheated so thatthe desired effects are secured in the maximum degree. It should beunderstood, however, that a useful result may be secured withoutadhering to this arrangement, for if one stream is cooled and dried andanother heated, mixture of the streams in the fan 'results in reheatingof the first stream after moisture has been rejected.

Referring now to Fig. 1.

The Walls 6 enclose a room or other space to be conditioned. The returnair duct 8 leads from the room to the intake end of the conditionerhousing 9, from which a total volume fan driven by motor l2, draws airand returns it to the room through the duct l3. Mounted in the housing 9are two coils l4 and I5, conventionally represented as sinuous coils. Itis immaterial to the invention what particular type of coil is used. Inthe air conditioning art it is customary to use finned tubes so asto geta large heat transfer surface,

The suction line N5 of a refrigerative circuit, leads to the suction ofcompressor I! which is driven through a belt l8 by an electric motor |9.This motor is started and stopped by an electrically controlled startingswitch, diagrammatically indicated at 2|. The compressor dischargesthrough the pipe 22 and branch pipe 23 to a combined condenser andreceiver 24, from which the liquid line 25 leads. The fittings indicatedat 26 are normally-open stop valves.

Branch pipe 2'! leads from the discharge pipe 22. The discharge end ofthe coil I4 is permanently connected with the suction line I6. Thedischargeend of the coil l5 leads to a T or junction 28 which isselectively connectedwith the suction line I6 or with the high pressurebranch line 21 by valves 29 and 3|, so arranged that when one is openedthe other is closed. The valve 29 is actuated by the energization anddeenergization of a winding 32, while the valve 3| is similarly actuatedby a winding 33. The valves are each biased in closing direction andeach is opened only when its related coil is energized. The two windings32 and 33 are selectively energized by a switch mechanism, hereinafterdescribed.

When the valve 29 is open and the valve 3| is closed, coil I5 isconnected to suction line |6, but when the valve 3| is opened and thevalve 29 is closed coil I5 is connected to the high pressure branch pipe21. The liquid line 25 leads to two automatic expansion valves, 34 whichcontrols the supply of refrigerant to the coil H, and 35 which controlssupply of refrigerant to the coil |5. Since these two valves arestructurally identical it will suffice to describe the valve asillustrated in section in Fig, 3, and then describe its connections, theconnections for the two valves being different.

Liquid refrigerant is supplied through line 25 tothe connection 36 andis delivered to the connected evaporator coil through the connection 31.

,Flow from connection 36 to connection 31 is controlled by a. poppetvalve 38 which seats in the direction of flow. This valve is connectedto a stem 39 and is urged in a valve closing direction,

by a coil compression spring 4|. The stress on this spring is adjustableby means of nut 42 which is threaded on a portion of the housing, asclearly shown in Fig. 3. The stem 39 is in thrust relation with aflexible diaphragm 43 which is subject on its lower face to fluidpressure in the chamber 44. The chamber 44 is isolated from thedischarge connection 37, a packing gland being arranged to seal the stem39, as clearly indicated in the drawings.

The chamber 44 is subject to pressure arriving through a pressureconnection 45. The space above the diaphragm 43 is subject to fluidpressure arriving through the connection 46, the temperature connection.

Reverting now to Fig. 1, it will be observed as to the valve 34 that apipe 41 leads from the pressure connection 45 to the discharge of coill4, so that the chamber 44 in valve 34 is always subject to suctionpressure. The pipe 48 leads from the temperature connection 46 to athermostatic bulb 49 in thermal conducting relation with the outlet ofthe coil I4. It will be observed, therefore, that the valve 34functionsv in response to superheat at the outlet of the coil I4.

The connections for the valve 35 are slightly different. A pipe 5| leadsfrom the pressure connection 45 to the outlet of the coil I5, from whichit results that if valve 29 is opened and valve 3| closed, the chamber44 of valve 35 is at the suction pressure in the system, but if valve 3|is opened and valve 29 is closed, the chamber 44 is subject to thedischarge pressure in the system, with the result that valve 38 thenwill be held continuously closed. Pipe 52 leads from the temperatureconnection 46 of valve 35 to a thermostatic bulb 53 which is not placedadjacent the discharge of coil l5 but is in thermal conducting relationwith the suction line l6 beyond thevalve 29. The purpose of this is tolocate the thermostatic bulb 53 where it will be subjected to thesuction temperature of the system and never subjected to the much higherdischarge temperature. It will be observed, however, that when valve 29is opened and valve 3| closed, the flow resistance between the point ofconnection of the pipe 5| and the location of the thermostatic bulb 53,is negligible so that when the valve 35 is operative to supply liquidrefrigerant to the coil l5 the control will be substantially in responseto superheat at the outlet of the coil.

The arrangement described protects the thermostatic bulb againstoverheating, prevents it from tending to open the expansion valve 35when the valve 29 is closed, while the location of the connection of thepipe 5| insures that the expansion valve 35 will be maintained closedwhen the suction connection valve 29 is closed.

With the compressor running and the valve 29 closed and valve 3| opened,coil I5 serves as a condenser. Refrigerant then liquefied in the coil I5is fed to the coil H by way of the high side float valve 54 and thecheck valve 55.

Leads 56 and 51 from any suitable current source provide electriccurrent for operating the electrically actuated valves 29 and 3| and themotor control switch 2| which starts and stops motor l9.

Lead 51 is connected with a terminal of the control switch 2| and withone terminal of each of the windings 32 and 33. Lead 56 is connected tothe right hand contact of the thermostatic mercury tube switch 56 whichtilts clockwise to close when dry bulb temperature rises above a chosenvalue assumed for discussion to be F.

arcane;

assumed when temperature is below 80 and humidity is above The otherterminals of switches 58 and 59 are connected to line 60 which leads tothe second terminal of control switch 2| which therefore runs motor l9unless both switches 58 and 53 are open.

Valves 29 and 3| are biased to closed position and open only if theirrespective windings 32 or 33 be energized. The tilting thermostaticmercury tube switch 6! energizes these windings selectively, but onlywhen line 60 is energized by the closure of at least one of the switches58 or 59. Line 60 is connected to the middle contact of switch Bl,winding 32 to the lefthand contact and winding 33 to the righthandcontact. Thermostaticswitch 6| is set to a control point not above, andpreferably a few degrees below the control point of thermostatic switch58. For discussion 74 is assumed as the control point of switch 6| Belowthis temperature it tilts clockwise to energize winding 33 anddeenergize 32 as shown in Fig. 1, while above this temperature it tiltscounterclockwise and reverses this effect.

Assuming that the thermostats and the humidostats are set for the valuesmentioned, which values are merely illustrative, and that dry bulbtemperature is above 80, the compressor will run and will run whether ornot humidity is above or below 50%. Inasmuch as'the dry bulb temperatureis above the setting of the thermostat 6|, valve 29 is opened and valve3| is closed. Consequently both coils are connected to the suction lineand both operate at a normal suction pressure to cool the air passingthrough the housing 9. The amount of dehumidificatlon which will occurwill depend on humidity conditions in the room,

but under these conditions both cooling and humidification will occur.

Suppose now the dry bulb temperature in the room-falls below 80"vwhile-the relative humidity is above 50%.- This amounts to saying thatthermostatic switch 58 opens but humidostatic switch 59 remains closed.The compressor will continue a to run and the conditioning effect willbe unchanged. This action, however, can continue only until dry bulbtemperature falls to the setting of the thermostatic switch 6|, 1. e.,74". If at this time the relative humidity is still above 50% so thatthe humidostatic switch 53. is still closed, thecompressor will continuein action, and the thermostatic switch 6| will shift to close the valve29 and open valve 3i. This disconnects coil I5 from suction line it andconnects it with the discharge line 21. Warm high pressure refrigerantfrom the compressor I! will thenfiow through valve 3| to the coil IS inwhich it is condensed. The highpressure thus established in coil 15 willbe transmitted through pipe I to chamber 44 of expansion valve 35,- andwill hold valve 38 to its seat preventing the supply of liquidrefrigerant through liquid line to coil.

I5. The thermostatic bulb 53 will not interfere with this action becauseit is still subject to temperature in the suction line. Liquidrefrigerant condensed in the coil IE will flow through the expansionvalve 54 and'the check valve 55 to 0011- II, but the refrigerant soflowing will be insuflicient to supply all the refrigerant requiredby'the coil ll. Consequently the expansion valve 34 will supply theremainder under the control of the superheat at or near the bulb 49.

Thus both coils will operate to cool the air and to an extent todehumidify' the air when dry bulb temperature is high. If dry bulbtemperature falls to normal value and the system is keptin operationbecause humidity is high, the dry bulb temperature can be only slightlyreduced before low-limit thermostat 6| responds and converts the secondcoil l5 from an evaporator coil to a condenser coil. When this occursthe suction pressure in the systemdrops because the compressor operatesat constant speed and the total amount of refrigerant fed through thecoil I l is less than the amount of refrigerant fed through both coilsl4 and I5 when they were both operating as evaporators. Consequentlyless heat is abstracted from theair but it is abstracted at a lowertemperature so that more latent heat and less sensible heat is'abstracted.

This intensifies the dehumidifying effect and diminishes, but does noteliminate, the cooling effect of the coil l4. However, the sensiblecooling caused by the coil I4 is counteracted by the reheating effect ofthe coil l5 which operates as a condenser and consequently rejects heatinto the air stream.

The above operative sequences are mentioned ous to recount in detailwill occur from time to I time. Such control cycles can be readilydeduced and will conform to the requirementsv imposed.

An important point is that the system can operate to dehumidify withoutsubstantial reduction in dry bulb temperature. This results in importanteconomies. The humidity control is in response to relative humiditywhich is a function of dry bulb temperature. To secure the desiredrelative humidity, but at a lower dry bulb temperature entails anunnecessary and wasteful removal of atmospheric moisture for it does notimprove comfort conditions. Hence, maintenance of the dry bulbtemperature, reduces the latent heat load and improves the operative'efllciency as compared to a system in which relative humidity is heldconstant and dry bulb temperature is reduced as an incident todehumidiflcation.

A further development of. this idea by the use of a modifying controlsubject to outdoor ternperatures to secure the maximum practicableeconomy under varying summer conditions, is a feature of the elaboratedembodiment shown in Fi 2. s v

Fig. 2 shows all the components of Fig. 1 with certain additions andrefinements particularly in the automatic controls.

,Identical parts in Fig. 2 are given the same reference numerals as inFig. 1. Modified control elements are given the same number with 'theletter a. New components are distinctively motor Bld. The operatingrange of Bic may be from' a low limit approximating the lowest outdoortemperature at which cooling is needed, to Y a high summer temperature.The resulting adjustment of the control point is from a low value, say74 when outdoor temperature is low, to a value slightly below thecontrol point of thermostat 58, say 79 when outdoor temperature is high.

Thus on hot days the controls are set to take the utmost practicableadvantage of the economy secured by limiting dehumidification to thatessential for comfort, while on cooler days cooling and dehumidificationare allowed to continue to lower values of temperature. The readjustmentcan, of course, be made manually, if preferred.

At the entrance end of conditioner housing 9 spray heads 62 are added.These are supplied with water under pressure through connection 63 undercontrol of valve 64 which is biased to closed position and opened byenergizing winding 65, one of whose terminals is connected to lead 51.The other terminal of the winding is connected with the middle terminalof the low limit humidostat mercury tube switch 66, whose left-handterminal is connected with lead 56. The control point of humidostat 66is low, say 40% relative humidity, below which value the switch shiftsfrom the position shown in Fig. 2, counterclockwise to close a circuitfrom 56 to 51 through winding 65 thus opening valve 64 and operating thespray heads.

The humidostat 59a. differs from humidostat 59 of Fig. 1 only in that ithas a third (left-hand) contact which is connected to the right handcontact of low limit humidostatic switch 66. Thus if temperature ishigh, so that switch 58 energizes line 60 and humidity is low so thatswitch 590. is tilted counterclockwise, there will be a circuit from 56to 60 (via switch 58) through left contact of switch 59a to rightcontact of switch 66 through winding 65 to line 57. This operates thesprays whenever they would perform adiabatic cooling because of high airtemperature and low relative humidity.

Eliminators 61 are used to remove entrained water droplets from the airstream. A heater coil 68 is mounted in the exit end of housing 9. Itmight be of any controllable type, but is assumed to be a steam coilcontrolled by the normally closed valve 69 fed with steam by line H andopened by energizing winding I2. One terminal of this winding isconnected with lead 51, the other with the right hand contact ofthermostatic mercury tube switch 13 whose other contact is connectedwithlead 56. This switch closes the circuit and admits steam to coil 68 iftemperaturefalls below a chosen point,

say 70 F.

The system disclosed in Fig. 2 has the same functions as the system ofFig. 1 and certain added functions in addition to the readjustmentfeature above discussed. The thermostat 13 controls heating means. Thelow limit humidostat 66 operates the sprays 62 whenever humidity fallsbelow a chosen low value, or whenever thermostat 58 calls for coolingand humidostat 59 does not call for dehumidification. Thus someadiabatic sensible cooling is secured by the use of the sprays duringthe cooling season whenever dehumidification is notrequired. The samesprays maintain a minimum relative humidity during the heating season.

Two specific embodiments have been described and others within the scopeof the invention can be evolved by the exercise of mechanical skill.

The valves 29 and 3| conjointly perform the function of a three-wayvalve arranged to connect the discharge of coil I5 selectively withlines l6 and 21, as will be obvious to those skilled in the art.

What is claimed is:

1. The method of controlling an air conditioning plant of therefrigerative circuit type in which air to be conditioned exchanges heatwith two surface heat exchangers connected in said circuit, whichcomprises operating both exchangers as evaporators when cooling ischiefly required, and when dehumidification is chiefly requiredoperating one exchanger as an evaporator and the other as a. condenser.

'2. The method of controlling an air conditioning plant of therefrigerative circuit type in which air to be conditioned exchanges heatwith a first surface heat exchanger and then with a second surface heatexchanger both connected in said circuit, which comprises operating bothexchangers as evaporators when cooling is chiefly required, and whendehumidification is chiefly required operating said first exchanger asan evaporator and said second exchanger as a condenser.

3. The method of controlling an air conditioning plant of therefrigerative circuit type in which air to be conditioned exchanges heatwith two surface heat exchangers capable of operating as evaporators,which comprises operating both exchangers as evaporators at a normalsuction pressure when cooling is chiefly required, and whendehumidification is chiefly required operating one exchanger as anevaporator at a lower suction pressure than said normal and at the sametime operating the other heat exchanger as a condenser.

4. The method of controlling an air conditioning plant of therefrigerative circuit type in which air to be conditioned exchanges heatwith two surface heat exchangers serially, both said exchangers beingcapable of operating as evaporators, which comprises operating bothexchangers as evaporators at a normal suction pressure when cooling ischiefly required, and when dehumidification is chiefly requiredoperating the exchanger first affecting the air as an evaporator at alower suction pressure than said normal, and the other exchanger as acondenser.

5. The method of controlling an air conditioning plant of therefrigerative circuit type in which air to be conditioned exchanges heatwith two surface heat exchangers capable of operating .as evaporators,which comprises operating both exchangers as evaporators when cooling ischiefly required, and when dehumidification is chiefly requiredoperatirg one exchanger as an evaporator and at the same time operatingthe other heat exchanger as a condenser, and supplying refrigerant socondensed to the exchanger which operates as an evaporator.

6. The method of controlling an air conditioning plant of therefrigerative circuit type in which air to be conditioned exchanges heatwith two surface heat exchangers serially, the exchangers forming partsof said circuits, which comprises operating both exchangers asevaporators when cooling is required; when temperature in theconditioned space is depressed below normal and humidity in theconditioned space is above normal, operating the exchanger firstaffecting the air as an evaporator and the other exchanger as acondenser; and adjusting the permissible depression of temperature belownormal according to outdoor temperature.

7. In an air conditioning system, the combination of a refrigeratingcircuit having evaposive to temperature and to humidity for, keepingsaid circuit in operation when temperature or humidity or both exceedchosen values; and temperature responsive means controlling theoperative characteristics of said circuit and effective at a limitingtemperature below the above named chosen value, to reduce thetemperature of at least a portion of said evaporator and cause thecircuit to reject heat to the conditioned air.

8. In an air conditioning system', the combination of a refrigeratingcircuit having an evapo rator, and means for circulating air to beconditioned thereover, said circuit serving to absorb heat from airbeing conditioned through said evaporator and reject said heat; meansresponsive to temperature and to humidity for keeping said circuit inoperation when temperature or humidity or both exceed chosen values;temperature responsive means controlling the operative characteristicsof said circuit and effective at a limiting temperature below the abovenamed chosen value, to reduce the temperature of at means forcirculating air to be conditioned; a

refrigerative circuit including a heat exchanger in the path ofcirculating air; converting means means for circulating air to beconditioned; a

refrigerative, circuit including a heat exchanger .in the path ofcirculating air; converting means for selectively establishing twooperative conditions in one of which the exchangerserves as arefrigerative evaporator to abstract heat and in the other of which aportionof the exchanger serves as a refrigerative evaporator to abstractheat, and another portion serves as a condenser to reject heat to-thecirculating air; means responsive to the temperature of conditioned airfor controlling said converting means; and means responsive to outdoortemperature serving to vary the temperature at which the last-namedmeans actuates said converting means.

11. In an airconditioner, the combination of two surface heatexchangers; means for circulating air to be conditioned in heat exchangerela- 1 tion with said exchangers; a constant speed compressor; acondenser; and means for connecting said exchangers in circuit with saidcompressor and condenser, in two relations, in one of which bothexchangers operate as, evaporators, and 'in theother of which oneoperates as an evaporator and the other as a condenser.

12. In an air conditioner, the combination of two surface heatexchangers; means for circulating air to be conditioned in 'heatexchanging relation with one of said conditioners and then with theother thereof; a constant speed compressor;

changers in circuit with said .compressor and condenser in tworelations, in one of which both exchangers operate as evaporators, andin the other of which the exchanger which first afiects the air operatesas an evaporator and the other exchanger operates as a condenser.

13. man air conditioner, the combination of two surface heat exchangers;means for circulating air to be conditioned in heat exchange relationwith said. exchangers; a constant speed compressor; a condenser; meansfor connecting said exchangers in circuit with said compressor andcondenser in two elations, in one of which both exchangers operate asevaporators, and in the other of which one operates as an evaporator andthe other as a condenser; and means for supplying refrigerant condensedin the last-named exchanger to the other exchanger. Y

14. In an air conditioner, the combination of two surface heatexchangers; means for circulating air to beconditioned in heat exchangerelation with said exchangers; a compressor; a condenser into which saidcompressor discharges; a suction line connecting one of said exchangerswith the suction of the compressor; valve means for selectivelyconnecting the other of said exchangers with the suction and with thedischarge of said compressor; and two automatic expansion valvesarranged to feed liquid refrigerant from said condenser to respectiveexchangers, said expansion valves including temperature responsive meanssubject to temperature in the suction line and pressure responsive meanssubject to pressure in the respective related exchangers.

15. In an air conditioner, the combination of two surface heatexchangers; means for circulating air to be conditioned in heat exchangerelation with said exchangers; a constant speed compressor; a condenserinto which said compressor discharges; a suction line connecting one ofsaid exchangers with the suction of the compressor; valve means forselectively connecting the other of said exchangers with the suction andwith the discharge of said compressor; two automatic expansion valvesarranged to feed liquid refrigerant from said condenser to respectiveexchangers, said expansion valves including temperature responsive meanssubject to temperature in the suction line and pressure responsive meanssubject to pressure in the respective related exchangers; and means forfeeding liquid refrigerant from said other exchanger to the flrstnamedexchanger. 1

16. In an air conditioner) the combination of two surface heatexchangers; means for circulating air to be conditioned in heat exchangerelationwith said exchangers; a compressor; a cona condenser; and meansfor connecting said exdenser into which said compressor -discharges; a

pansion valves including temperature responsive means subject totemperature in the suction line and pressure responsive means subject topres-.

lating air to be conditioned in heat exchange relation with saidexchangers; a compressor; a condenser; means for connecting saidexchangers in circuit with said compressor and condenser in tworelations, in one of which both exchangers operate as evaporators and inthe other of which one operates as an evaporator and the other as acondenser; controlling means responsive to temperature and to humidity,arranged to stop said compressor when humidity and temperature are bothnormal and to run said compressor when either or both humidity andtemperature are high; and temperature responsive means functionallyrelated to said controlling means and in conjunction therewithcontrolling the means for connecting the exchangers to establish thesecond-named relation when humidity is high and temperature concurrentlyfalls below normal and to establish the first-named relation at othertimes.

18. In an air conditioner, the combination of two surface heatexchangers; means for circulating air to be conditioned in heat exchangerelation with said exchangers; a constant speed compressor; a condenser;means for connecting said exchangers in circuit with said compressor andcondenser in two relations, in one of which both exchangers operate asevaporators and in the other of which one operates as an evaporator andthe other as a condenser; controlling means responsive to temperatureand to humidity, arranged to stop said compressor when humidity andtemperature are both normal and to run said compressor when either orboth humidity and temperature are high; and temperature responsive meansfunctionally related to said controlling means and in conjunctiontherewith controlling the means for connecting the exchangers toestablish the second-named relation when humidity is high andtemperature concurrently falls below normal and to establish thefirstnamed relation at other times. i 19. In an air conditioner, thecombination of two surface heat exchangers; means for circulating air tobe conditionedin heat exchange relation with said exchangers; acompressor; a condenser; means for connecting said exchangers in circuitwith said compressor and condenser in two relations, in one of whichboth exchangers operate as evaporators and in the other of which oneoperates as an evaporator and the other as a condenser; controllingmeans responsive to temperature and to humidity, arranged to stop saidcompressor when humidity and temperature are both normal and to run saidcompressor when either or both humidity and temperature are high;temperature responsive means functionally related to said controllingmeans and in conjunction therewith controlling the means for connectingthe exchangers to establish the second-named relation when humidity ishigh and temperature concurrently falls below normal and to establishthe first-named relation at other times; and means responsive to outdoortemperature, and serving to adjust the control point of the last-namedtemperature responsive means.

20. In an air conditioner, the combination of two surface heatexchangers; means for circulating air to be conditioned in heat exchangerelation with said exchangers; a compressor; a

condenser; means for connecting said exchangersa condenser; controllingmeans responsive to temperature and to humidity, arranged to stop saidcompressor when both humidity and tem perature do not exceed normal andto run said compressor at other times; temperature responsive meansfunctionally related to said controlling means .and in conjunctiontherewith controlling the means for connecting the exchangers toestablish the second-named relation when humidity is above normal andtemperature concurrently is below normal and to establish thefirst-named relation at other times at least when the compressor runs;normally inactive means for spraying water into the air approaching saidheat exchangers; and means responsive to humidity and serving whenhumidity is abnormally low to cause said spraying means to operate.

21. In an air conditioner, the combination of two surface heatexchangers; means for circulating air to be conditioned in heat exchangerelation with said exchangers; a compressor; a condenser; means forconnecting said exchangers in circuit with said compressor and condenserin two relations, in one of which both exchangers operate as evaporatorsand in the other of which one operates as an evaporator and the other asa condenser; controlling means responsive to temperature and tohumidity, arranged to stop said compressor when both humidity andtemperature do not exceed normal and to run said compressor at othertimes; temperature responsive means functionally related to saidcontrolling means and in conjunction therewith controlling the means forconnecting the exchangers to establish the second-named relation whenhumidity is above normal and temperature concurrently is below normaland to establish the first-named relation at other times at least whenthe compressor runs; normally inactive means for spraying water into theair approaching said exchangers; and means responsive to humidity andoperatively related to said controlling means for operating said sprayswhen humidity is abnormally low and also when humidity is normal andtemperature is high.

22., In an air conditioner, the combination of two surface heatexchangers; means for circulating air to be conditioned in heat exchangerelation with said exchangers; a compressor; a condenser; means forconnecting said exchangers in circuit with said compressor and condenserin two relations, in one of which both exchangers operate as evaporatorsand in the other of which one operates as an evaporator and the other asa condenser; controlling means responsive to temperature and tohumidity, arranged to stop said compressor when both humidity andtemperature do not exceed normal and to run said compressor at othertimes; temperature responsive means functionally related to saidcontrolling means and in conjunction therewith controlling the means forconnecting the exchangers to establish the second-named relation whenhumidity is above normal and temperature concurrently is below normaland to establish the first-named relation at other times at leastwhenthe compressor runs; normally inactive means for supplying heat tothe circulating air; and means responsive to an abnormally lowtemperature for rendering the last-named means active.

23. In an air conditioner, the combination of two surface heatexchangers; means for circulating air to be conditioned in' heatexchange relation with said exchangers; a compressor; a condenser; meansfor connecting said exchangers in circuit with said compressor andcondenser in two relations, in one of which both exchangers operate asevaporators and in the other of which one operates as an evaporator andthe other as a condenser; controlling means responsive to temperatureand to humidity, arranged to stop said compressor when both humidity andtemperature do not exceed normal and to run said compressor at othertimes; temperature responsive means functionally related to saidcontrolling means and in conjunction therewith controlling the means forconnecting the exchangers to establish the second-named relation whenhumidity is above normal and temperature concurrently is below normaland to establish the first-named relation at other times at least whenthe compressor runs; normally inactive means for spraying water into theair approaching said heat exchangers; means responsive to humidity andserving when humidity is abnormally low to cause said sprays to operate;normally inactive means for supplying heat to the circulating air; andmeans responsive to an abnormally low temperature for rendering thelast-named means active.

24. In an air conditioning system, the combination of a refrigeratingcircuit including a compressor operated at substantially uniformcapacity, an evaporator and means for circulating air to be conditionedthereover, said circuit serving to absorb heat from the air beingconditioned through said evaporator and reject said heat; meansresponsive to relative humidity arranged to cause and suspend theoperation of said circuit as relative humiditypasses above and below achosen value; means operable to limit the total liquid refrigerantsupplied to said evaporator, whereby at least a portion of theevaporator will be caused to operate at an abnormally low suctionpressure; and means responsive to reduction of temperature of theconditioned air below a limiting temperature serving to cause thecircuit to deliver rejected heat to the air after its heat exchange withthe evaporator, and serving also to operate said liquid refrigerantsupply limiting means.

25. In an air conditioning system the combination of a refrigeratingcircuit including a compressor operated at substantially uniformcapacity, an evaporator and means for circulating air to be conditionedthereover, said circuit serving to absorb heat from the air beingconditioned through said evaporator and reject said heat; meansresponsive to temperature and to relative humidity arranged to causeoperation of said circuit when temperature or relative humidity or bothexceed chosen values and to suspend the operation of said .circuit whenboth are below such values; means operable to limit the total liquidrefrigerant supplied to said evaporator, whereby at least a portion ofthe evaporator will be caused to operate at an abnormally low suctionpressure; and means responsive to reduction of temperature of theconditioned air below a chosen temperature lower than the above-namedtemperature value to cause the circuit to deliver rejected heat to theconditioned air and serving also to operate said liquid refrigerantsupply limiting means.

lable operating means for Withdrawing refrigerant'from said evaporatorand delivering it at higher pressure to said condensing means; meansoperable to cause said evaporator to operate at an abnormally lowpressure and to cause said exchanger to deliver. heat to the air;control means responsive to conditions in said space and comprisingtemperature responsive and humidity responsive means: and connectionswhereby said control means controls the operating means for therefrigerating system and also controls the

